Guy Norris/LOS ANGELES

McDONNELL Douglas (MDC) is preparing to flight-test a new package of aerodynamic improvements to be incorporated into the MD-11ER variant from 1996 onwards.

The modifications are aimed at achieving further drag reductions and cuts in fuel consumption as part of Phase IV of the MD-11 continuous-performance-improvement package (PIP). The modifications are due to be available early in 1996, to coincide with entry into service of the 286,250kg maximum-take-off-weight MD-11ER version.

The changes will follow hot on the heels of the introduction of the TOPAZ computerised take-off-performance analysis system which will be certificated by the US Federal Aviation Administration and the European Joint Airworthiness Authorities (JAA) in the first quarter of 1996.

Of the 1.2% drag-reduction target set by MDC for Phase IV, some 0.5% has already been achieved through improvements to the flap-hinge fairings and seals. Another 0.4% has been gained through alterations to the horizontal elevator bias.

"There is still a measurable amount to go," says MD-11 general manager Jim Bouey, who adds that test results from other drag-reduction ideas, such as the aft-fuselage strake and diverter fillet, were disappointing (Flight International, 21 December, 1994-3 January, 1995).

"The diverter fillet and fuselage strakes didn't work out, but now we're getting to the point where the aircraft is so slick that we have to challenge the notion that we'll get much more out of it," says the company.

In addition to the modifications already tested and accepted, MDC intends to flight test the following:

a revised tail-cone shape. MDC's computational fluid dynamics of new tail-cone shapes indicates that a "flared-out" tailcone will produce a new pressure distribution with less drag. The flare will be made aft of the rear-most structural join in the all-composite unit;

changes to the fillet area of the upper surfaces of the trailing edge of the wing;

a new modification to the engine pylon where it intersects with the upper surface of the nacelle (particularly on the Pratt & Whitney-powered versions).

Extension of the wing-pylon fillet modification devised and offered under an earlier improvement programme, which nets a 1% performance improvement;

possible use of vortex generators on the wing outboard section.

The total package, including features already "locked into" the Phase IV programme, will be flight-tested for the next three months. "Hopefully, we'll get enough to reach our 1.2% target," says Bouey. "We have committed to have the MD-11ER available by the first quarter of 1996, and this is one element of it," he adds.

The ER version will have its range extended by up to 945km (510nm), to 13,900km and a maximum take-off weight 2,270kg over that of current models.

MDC and Aviation Partners, the Washington-based winglet maker, are studying the possible use of its blended and spiroid winglets on the MD-11. The winglets, which have been developed as part of work aimed primarily at corporate jets like the Gulfstream III, could reduce fuel consumption by up to 6%, says the company.

Source: Flight International